1. Field of the Invention
The invention relates to a device for comminuting scrappable feedstock by way of cutting or shear-cutting.
2. Description of the Background Art
The comminution of feedstock is a central component of mechanical process engineering, in which a source material is reduced into smaller components by a separation operation. The feedstock is thereby changed in size, shape or composition with regard to its later use. An example of this would be the preparation of waste material, in which the source material must be reduced in size in order to be processed in subsequent processing stations, or in which the feedstock is simultaneously separated into different fractions thereof, following comminution.
The invention relates to the field of comminution technology, in which the comminution work is performed primarily by cutting and shear-cutting, i.e. the active edges of two tools are run past each other while maintaining a narrow gap. The feedstock must therefore be cuttable, which rules out the use of mineral materials for comminution. Suitable tools are, for example, rotary disks mounted on a rotor whose cutting edges run along the disk circumference and which interact with directly adjacent rotary disks. It has been demonstrated that portions of the feedstock become wedged in the spaces formed by the rotary disks or, in the case of fibrous or wire-shaped feedstock, are wound around the drive shaft. These portions therefore not only fail to be comminuted, but they also greatly interfere with the smooth comminution of the remaining feedstock. These portions must therefore be removed from the rotor at regular intervals, which involves painstaking and time-consuming manual labor. In addition to the labor costs associated therewith, machine down times caused thereby must also be taken into account, which negatively impacts the overall economic feasibility of devices of this type.
To remedy this situation, a device is known from EP 0 760 251 A1, the cutting tool of which comprises two counter-rotating rotors on which are mounted meshing cutting disks. Scraping elements which run along the side housing wall on a radial plane are attached in the area of the axial distance between two cutting disks, the projecting ends of these scraping elements having an edge of concave design which follows the shaft circumference. The scraping elements perform the function of removing feedstock located in the space from the rotor in the radial direction.
The disadvantage of devices of this type is caused by the machine construction. By attaching the scraping elements to the side walls of the housing, the forces acting upon the scraping elements are introduced directly into the housing. The side walls must therefore be reinforced accordingly, which is ordinarily done by means of complex ribbed wall constructions.
To introduce these forces into the housing walls as safely as possible, the scraping elements have an approximately triangular shape, the base of the triangle being used for attachment to the side wall. To nevertheless obtain an obtuse angle of connection to the drive shaft in a scraping element design of this type, in order to achieve a lifting effect for the feedstock to be removed, it is necessary for the scraping elements to relatively broadly surround the shaft. Known scraping elements are therefore designed with a correspondingly large size.
Furthermore, the side attachment of the scraping elements, together with the radial overlapping of the two rotors in the central region of the device, produces a barrier for the feedstock which runs at the height of the rotors and prevents the material from flowing freely to the side between the rotor and the housing. This is disadvantageous, particularly in reversing mode, since interfering feedstock cannot be automatically removed from the device and therefore causes an operational shutdown.
A device according to the definition of the species is known from DE 10 2005 026 816 A1, the cutting tool of which is also formed by two counter-rotating rotors which run parallel to the axis. Cutting disks which are fitted with knives at an axial distance along the circumference and perform the comminution work in interaction with counter-knives are mounted on the rotors. First counter-knives are situated along the housing wall and are permanently connected thereto; second counter-knives are mounted centrally on a cross member beneath the cutting tool in the radial overlapping area of the two rotors. Scraping elements whose free ends extend radially into the space between two cutting disks, where they interact with rotating knives on the cutting disks, are integrated into the counter-knives.
As in the prior publication cited above, a disadvantage also arises here from the attachment between the counter-knives and the housing walls. Strong forces are thereby introduced into the side housing parts, which, in turn, necessitates a stable and complex design of the housing walls.
In addition, the counter-knives and cutting tool again form a continuous barrier at the height of the rotors, which makes it impossible in reversing mode to automatically remove interfering feedstock from the device. The cross-member in the area of the material passage between the two rotors also provides an increased resistance to flow which hinders the material in flowing through the device.